Interpretive Summary: Despite being known mainly as a disease agent in mammals, S. agalactiae has become recognized as an emerging pathogen of wild and cultured fish and bottlenose dolphins. Previously, using serological and multilocus sequence typing (MLST) molecular techniques, we discovered that the Kuwait dolphin and piscine lineage (serotype Ia, Sequence type-7) was also associated with human neonatal infections in Japan. These findings suggested that isolates derived from humans have the potential to cause disease in different animal species. This study examined the potential for a human S. agalactiae isolate to experimentally cause disease in fish.

Technical Abstract:
Streptococcus agalactiae, the Lancefield group B Streptococcus (GBS), long recognized as a mammalian pathogen, is an emerging pathogen to fish. We show that a GBS serotype Ia, multilocus sequence type ST-7 isolate from a human neonatal meningitis clinical case causes disease signs and mortality in Nile tilapia, Oreochromis niloticus.